A conventional check valve has a case where a fluid passage and a valve seat are formed, a valve member that touches and separates from the valve seat to open and close the fluid passage, and a spring that energizes the valve member in a valve-closing direction.
Further, the check valve is opened when an energization force of fluid in a valve opening direction exceeds an energization force of the spring in a valve closing direction.
Moreover, the valve member has a piston part that reciprocates and a valve part that touches to and separates from the valve seat. The piston part and the valve part are unified, and the piston part is accommodated in the case reciprocatably (refer to Japanese Patent Application Laid-Open Publication No.9-20218, for example),
A braking system that controls a brake fluid pressure of a ABS control (anti-skid control) of a vehicle has a brake fluid pressure generating means that generates the brake fluid pressure based on an operation of a braking member, and a pump that pumps the brake fluid from a low pressure area and discharges the high-pressurized brake fluid.
The conventional check valve mentioned above is used, for example, as a discharge valve of the pump in the braking system.
In that case, the check valve is disposed between the brake fluid pressure generating means and the discharge side of the pump, and permits the flow from the pump to the brake fluid pressure generating means when the pump is operating, while a braking pressure of a regular braking system is prevented from falling out to the low pressure area through the pump during a regular braking when pump is not operating.
However, in the conventional check valve, if the piston part sticks within the case due to a foreign substance when the valve is opened, since the valve part cannot sit onto the valve seat (i.e., the valve is not closed) even if the pressure in the lower stream side of the fluid flow becomes higher than the pressure in the upper stream side of the fluid flow, there is a problem that fluid would flow backwards.
Moreover, if the piston part gets stuck and does not close the valve as mentioned above when the conventional check valve is used as a discharge valve of the pump in the braking system, since the braking pressure of regular so braking system reduces to the pressure of the low pressure area through the pump during regular braking, there is a problem that the brakes during regular braking became weak.